A method of manufacturing a solar energy absorbing film often includes an evaporation process, a sputtering process, or an electrodeposition process. The quality of the solar energy absorbing film formed by a co-evaporation process or a sputtering process in vacuum-based processes is superior than that of the solar energy absorbing film formed by a traditional electrodeposition. Moreover, the vacuum-based process can produce the solar energy absorbing film having compact, dense, crystalline, uniform, continuous and large grain-size characteristics. However, the apparatus of the vacuum processes is very expensive.
In those methods of manufacturing the solar energy absorbing film formed by a copper (Cu) element, an indium (In) element and a selenium (Se) element (CIS), one of them is to co-vapor the Cu, In elements firstly, and then anneals the Cu, In elements or a deposition layer formed by the Cu and In elements as a precursor. The co-evaporation includes two steps. Firstly, the Cu, the In and the Se are co-vapored to form a CIS layer, which is copper-rich on a substrate at a lower temperature (450° C.). Secondly, a thin film is deposited which is indium-rich on the CIS layer at higher temperature (550), and causing the CIG layer to lack the Cu as a whole for improving a filling factor of the solar energy absorbing film.
Another method of manufacturing the solar energy absorbing film is a selenium-combining process of a metal precursor layer. At first, the metal precursor layer is sputtered, vaporized, or electrodeposited, and then the selenium-combining is performed on the metal precursor layer by using a thin hydride selenium. The above method can improve a surface quality and reduce shallow defects, but the hydride selenium is a poisonous gas, and would be harmful to human health when the gas is leaked carelessly. Therefore, there is continuous improvement on new processing techniques, which fulfill the four criteria: the low cost, the high material yield, the scalability and the manufacturability.
The traditional electrodepositing process has a benefit of low cost; however, the quality of the solar energy absorbing film formed by the electrodepositing process is less superior to that of the solar energy absorbing film formed by the vacuum-based process, thereby resulting in a poor photoelectric conversion efficiency of the solar energy absorbing film.
If the defects in the solar energy absorbing film of the solar cell are too many, a mass recombination center will be formed therein by recombining electrons and electron holes which are excited by the sun light previously, and that will reduce a generation of a photo current and the photoelectric conversion efficiency of the solar cell. Thus, the amount of the defects in the solar energy absorbing film should be minimized as possible as it can be. However, when the solar energy absorbing film is manufactured by the traditional electrodepositing process, the defects and lots of voids can form a problem due to the inferior crystalline and the lack of the compaction.
In order to improve the quality of the solar energy absorbing film manufactured by the traditional electrodepositing process, one technique in prior art is to heat the solar energy absorbing film, and then an anneal process is adopted later. Another technique is to co-electrodeposit to form the CIS layer, and then an order vacancy compound (OVC) is sputtered or vaporized on the CIS by the vacuum-based process. For the methods in the prior art, such as the vacuum-based process or using different electrolytic solution to electrodeposit, no matter what technique is adopted, the last step is of sputtering or electrodepositing a rich indium on the CIS to improve a filling factor (FF) of the solar cell, and those techniques are too complex or expensive. For examples, after co-electrodepositing, the rich indium is sputtered on the CIS by the vacuum-based process to create the OVC, the vacuum-based technique still cost expensively. However, after co-electrodepositing, the rich indium is electrodeposited on the CIS by replacing the electrolytic solution, there is also a need to perform the anneal process for crystallizing.